Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. PREDATOR INTERACTIONS WITHIN A TROPHIC LEVEL: PHALANGIUM OPILIO L. (ARACHNIDA: OPILIONES) AND MITES (ARACHNIDA: ACARI) _________________________________________ A thesis submitted in partial fulfilment of the Degree of Master of Applied Science at Lincoln University by C.N. Merfield _________________________________________ Lincoln University 2000 Page i Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science PREDATOR INTERACTIONS WITHIN A TROPHIC LEVEL: PHALANGIUM OPILIO L. (ARACHNIDA: OPILIONES) AND MITES (ARACHNIDA: ACARI) by C.N. Merfield Keywords: agroecosystem, Anystis baccarum, Balaustium spp., Calliphora stygia, commensalism, European harvestmen, klinokinesis, orthokinesis, P. opilio, predators, prey facsimiles, sentinel prey, This study investigated commensal feeding interactions between the European harvestman (P. opilio L.) and the predatory mites Balaustium spp. and Anystis baccarum L. It also investigated the feeding behaviour of P. opilio. Experiments were conducted in the laboratory using standardised temperature, humidity, photoperiod and experimental arenas, with eggs of the brown blowfly (Calliphora stygia F.) as prey facsimiles. Due to initial difficulties in obtaining enough predatory mites, mite feeding was manually simulated piercing blowfly eggs with a minuten pin. P. opilio consumed significantly more freeze-killed than live blowfly eggs, indicating that freezing induced chemical and/or physical changes to blowfly eggs that are detected by P. opilio. Significantly more manually pierced eggs were consumed by P. opilio compared with unpierced ones, demonstrating that piercing caused a chemical and/or physical to the egg and increased the feeding rates of P. opilio. Different densities of eggs had no effect on the numbers eaten by P. opilio and placing single pierced eggs next to groups of unpierced eggs also had no effect on the numbers of unpierced eggs eaten. These results suggest that P. opilio does not exhibit klinokinesis or orthokinesis to intensify its search for prey around the area where previous prey were located. P. opilio ate significantly more brown blowfly eggs that had previously been fed on by mites, demonstrating that a short term commensal interaction existed. However, further work is required to demonstrate if the relationship is commensal in the longer term. A comparison between hand-pierced and mite-pierced eggs showed that P. opilio ate Page ii significantly more of the former indicating that mite and hand piercing were quantitatively different. The potential for, and importance of, other commensal or mutual relationships between predators in agroecosystems is discussed. The lack of klinokinesis and orthokinesis in P. opilio is compared with other predators and parasitoids that do exhibit these behaviours. The means by which prey are detected by P. opilio are discussed in relation to interpreting behaviours such as prey inspection. Concerns about the effect of pre- treatment and handling of sentinel prey and the problems of using prey facsimiles are raised. Page iii Acknowledgements I would like to thank my supervisors Professor Steve Wratten and Mr Bruce Chapman for all their help and advice in the production of this thesis. I also strongly appreciate their tolerance of, and support for, the myriad other activities, most totally unrelated to this thesis, that I undertook during my time at Lincoln, some of which required the suspension of academic work for several months. My thanks also to Dr Chris Frampton, for his patient and humorous advice on all matters statistical, often at short notice. Warm thanks to all the members of the Ecology and Entomology Group. It is a truly wonderful place to work, study and play. Finally I would like to thank my flatmates Charlie and James for being the coolest people I could wish to live with. Page iv Contents Abstract ii Acknowledgements iv Contents v List of Tables viii List of Figures ix Chapter 1: Introduction 1 1.1 Global trends in agricultural production and pest management 1 1.2 Biological control in agroecosystems 2 1.3 Conservation biological control research in agroecosystems 3 1.4 Predation and parasitism theory 4 1.5 The roles of mites and harvestmen as predators in agroecosystems 6 1.6 Mite and harvestmen: trophic interactions in New Zealand 7 1.7 Arthropod predation behaviour and video recording techniques 9 1.8 Study aims 10 Chapter 2: Rationale for Experimental Design and Materials & Methods 11 2.0 Acclimatisation of P. opilio for experiments 11 2.0.1 Pre-experimental work 12 2.0.1 General experimental design 15 2.1 P. opilio ‘preference’ for pierced or unpierced, freeze-killed blowfly 18 eggs 2.2 P. opilio ‘preference’ for live or freeze-killed blowfly eggs 19 2.3 P. opilio ‘preference’ for pierced or unpierced live blowfly eggs 19 2.4 P. opilio ‘preference’ for live pierced and unpierced blowfly eggs, with 20 egg replacement 2.5 Rate of egg consumption, percentages of blowfly eggs eaten and mean 20 number eggs eaten 2.6 P. opilio ‘preference’ for blowfly egg position in a four-by-four grid 21 2.7 Effect of the proximity of pierced to unpierced blowfly eggs, on 21 predation of unpierced eggs by P. opilio 2.8 The effect of distance between blowfly eggs on the total consumption 23 of, and ‘preference’ for, pierced and unpierced eggs by P. opilio 2.9 P. opilio ‘preference’ for blowfly eggs previously pierced by mites 24 Page v 2.10 Mite collection 24 2.11 P. opilio ‘preference’ for live mite-pierced or manually pierced brown 31 blowfly eggs Chapter 3: Results 33 3.1 P. opilio ‘preference’ for pierced or unpierced, freeze-killed blowfly 33 eggs 3.2 P. opilio ‘preference’ for live or freeze-killed blowfly eggs 34 3.3 P. opilio ‘preference’ for pierced or unpierced live blowfly eggs 34 3.4 The effect of egg replacement on P. opilio ‘preference’ and 35 consumption of pierced and unpierced live blowfly eggs 3.5 The effect of egg replacement on consumption of live blowfly eggs 36 3.6 P. opilio ‘preference’ for egg positions in a four-by-four grid 40 3.7 P. opilio ‘preference’ for unpierced eggs with or without a pierced egg 41 in close proximity 3.8 The effect of distance between blowfly eggs on consumption of, and 42 ‘preference’ by the predator 3.9 P. opilio ‘preference’ for blowfly eggs previously pierced by mites or 44 controls 3.10 P. opilio ‘preference’ for Balaustium spp. pierced or manually-pierced 46 brown blowfly eggs Chapter 4: Discussion 47 4.1 P. opilio ‘preference’ for pierced or unpierced, freeze-killed blowfly 47 eggs 4.2 P. opilio ‘preference’ for live or freeze-killed blowfly eggs 49 4.3 The effect of egg replacement on P. opilio ‘preference’ and 50 consumption of pierced and unpierced live blowfly eggs 4.4 P. opilio ‘preference’ for egg positions in a four by four grid 51 4.5 P. opilio ‘preference’ for unpierced eggs with or without a pierced egg 52 in close proximity 4.6 The effect of distance between blowfly eggs on consumption rate of, 52 and preference by, the predator 4.7 P. opilio ‘preference’ for eggs previously pierced by mites / control 54 blowfly eggs 4.8 P. opilio ‘preference’ for eggs pierced by Balaustium spp. for manually 55 Page vi pierced brown blowfly eggs Chapter 5: Conclusion 57 5.1 Aspects of P. opilio feeding behaviour 57 5.2 Critique of methodology 59 5.3 Commensalism between arthropod predators in agroecosystems 63 5.4 Suggestions for future research 65 Chapter 6: References 67 Page vii List of Tables Table 1. Proportion and number of A. baccarum that ate blowfly eggs and the 26 mean number of eggs eaten ±SE in a no-choice or choice test with an immature pea aphid. Table 2. Proportion of eggs eaten, with one SE, out of the total number of eggs 39 used in the experiment. Page viii List of Figures Figure 1. Mean number of blowfly eggs eaten over a 12 h period by P. opilio 13 individuals that had been subjected to one to six days of starvation. Figure 2. Live uneaten brown blowfly egg and predated egg shell after being 15 eaten by a P. opilio individual. One graduation = 0.5 mm. Figure 3. Immature female P. opilio. 17 Figure 4. Immature male P. opilio. 17 Figure 5. Mean (±SE) survival of A. baccarum kept in individual Petri dishes. 27 Mites were fed one freeze-killed blowfly egg a day and some were given immature pea aphids as food. Mites were kept at 20° C with a 3° C range with a dark:light photoperiod of 8:16 hours. Figure 6. Balaustium spp. feeding on a live brown blowfly egg. One graduation = 30 0.5 mm Figure 7. Mean number (+ SE) of pierced and unpierced, freeze-killed blowfly 33 eggs eaten or inspected by P. opilio; see Section 3.1 for definitions. Figure 8. Mean (+SE) number of freeze-killed and live blowfly eggs eaten or 34 inspected by P. opilio. Figure 9. Mean numbers (+SE) of pierced and unpierced, live blowfly eggs eaten 35 or inspected by P. opilio. Figure 10. Mean number (+SE) of pierced and unpierced blowfly eggs eaten by 36 P.